ide: ht6560b: Fix cast to pointer from integer of different size

Integer passed as pointer to drvdata should be cast to unsigned long to
avoid warning (compile testing on alpha architecture):

    drivers/ide/ht6560b.c: In function ‘ht6560b_init_dev’:
    drivers/ide/ht6560b.c:318:27: warning:
        cast to pointer from integer of different size [-Wint-to-pointer-cast]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>